Azeotrope or azeotropic composition containing pentafluoropropane and water, and method for producing pentafluoropropane

ABSTRACT

An object of the present invention is to provide a method that can efficiently remove water contained in pentafluoropropane. Provided as a solution is a method comprising distilling a composition comprising pentafluoropropane and water to thereby extract pentafluoropropane with a water content higher than that of the composition as a first stream, and pentafluoropropane with a water content lower than that of the composition as a second stream.

TECHNICAL FIELD

The present invention relates to an azeotropic or azeotrope-likecomposition comprising pentafluoropropane and water, and a method forproducing pentafluoropropane with a reduced water content using thecharacteristic of the composition.

BACKGROUND ART

Alternative refrigerants, such as 1,1,1,2,2-pentafluoroethane (HFC-125)and difluoromethane (HFC-32), have been widely used as importantsubstances that replace CFC, HCFC, etc., which destroy the ozone layer.However, these are potent global-warming substances, and there is aconcern that the diffusion of these substances may affect globalwarming. As a measure against that, these substances are collected afteruse; however, not all of them can be collected, and diffusion by leakageetc. cannot be ignored. Alternatives by CO₂ and hydrocarbon substanceshave also been examined; however, CO₂ refrigerants have low efficiency,and large devices are required. Thus, there are many problems incomprehensive greenhouse gas emission reduction, including energyconsumption. Moreover, hydrocarbon substances have safety problems dueto their high flammability.

Pentafluoropropanes typified by 1,1,1,2,2-pentafluoropropane(HFC-245cb), 1,1,1,2,3-pentafluoropropane (HFC-245eb), and1,1,1,3,3-pentafluoropropane (HFC-245fa) are expected as refrigerantsthat can solve the above problems. In addition, their applications asenvironmentally preferable cleaning agents, foaming agents, propellants,heat transfer media, fire extinguishers, etc., are also expected.Furthermore, the use of some of these pentafluoropropanes asintermediates for producing 2,3,3,3-tetrafluoropropene (HFO-1234yf,CF₃CF═CH₂) and 1,3,3,3-tetrafluoropropene (HFO-1234ze, CF₃CH═CHF), whichare HFCs of olefins with a low warming coefficient, has attractedattention.

Pentafluoropropanes can be obtained by fluorinating correspondingchloride raw materials, such as 1,1,1,2,3-pentachloropropane(HCC-240db), 1,1,1,3,3-pentachloropropane (HCC-240fa), and1,1,2,3-tetrachloropropene (HCO-1230xa), with HF by a vapor-phase orliquid-phase process in 1 to 3 steps. In these methods, HCl is producedas a by-product, and it is difficult to convert 100% of chloride (rawmaterial) and HF. Accordingly, it is necessary to recycle them in thereaction process. When the reaction to remove HF from pentafluoropropaneis performed, it is necessary to remove the produced HF, which inhibitsnew HF elimination reaction. Applicable methods are water washing,distillation, etc. The simplest method of removing HF from a mixed gasof pentafluoropropane and HF is a method of absorbing HF with water.However, in this method, the treated pentafluoropropane is inevitablycontaminated with vapor mist, and water in an amount corresponding tothe vapor pressure.

In addition, pentafluoropropane is often contaminated with water derivedfrom various sources, such as water contained in the raw materials,water generated from the catalyst, and water remaining in the facility.

Water contained in pentafluoropropane affects the stability ofpentafluoropropane, the corrosiveness of the apparatus, the ability as arefrigerant, etc., and is thus one of the important factors for qualitycontrol. The method of removing water is particularly an importanttechnique.

Conventionally, a method using an adsorbent, such as a molecular sieve,is common. For example, PTL 1 described below discloses zeolite that canbe applied to the drying of HFC-245fa. However, in this method, it isgenerally necessary to treat gas with a relatively low waterconcentration at high speed, which requires the use of a largedehydration column. In addition, it is necessary to regularly reproduceand exchange the adsorbent. There is also a problem in that a largeamount of industrial waste is generated when the adsorbent is exchanged.

CITATION LIST Patent Literature

PTL 1: JP2011-83726A

SUMMARY OF INVENTION Technical Problem

The present invention was made in consideration of the current situationof the above prior art. A main object of the present invention is toprovide a method that can efficiently remove water contained inpentafluoropropane.

Solution to Problem

The present inventors conducted extensive research to achieve the aboveobject. As a result, the present inventors found a conventionallyunknown phenomenon in which pentafluoropropane and water formed aminimum azeotropic composition (which is called a heterophase azeotropiccomposition when two liquid phases are famed). Then, the presentinventors found that water contained in pentafluoropropane can beefficiently removed by using this characteristic. Thus, the presentinvention has been completed.

That is, the present invention provides the following azeotropic orazeotrope-like composition, and the following pentafluoropropane fromwhich water is removed.

Item 1.

An azeotropic or azeotrope-like composition comprising1,1,1,2,2-pentafluoropropane (HFC-245cb) and water.

Item 2.

An azeotropic or azeotrope-like composition comprising1,1,1,2,3-pentafluoropropane (HFC-245eb) and water.

Item 3.

The azeotropic or azeotrope-like composition according to Item 1,wherein HFC-245cb and water are contained in an amount of 90 to 100 mass% relative to the entire composition.

Item. 4

The azeotropic or azeotrope-like composition according to Item 1,wherein HFC-245eb and water are contained in an amount of 90 to 100 mass% relative to the entire composition.

Item. 5

A method for producing a composition comprising pentafluoropropane witha water content lower than that of a starting composition comprisingpentafluoropropane and water, the method comprising:

-   -   (1) distilling the starting composition to thereby extract a        pentafluoropropane-containing composition with a water content        higher than that of the starting composition as a first stream,        and a pentafluoropropane-containing composition with a water        content lower than that of the starting composition as a 30        second stream.

Item. 6

The method according to Item 5, wherein the distillation is performedwithin a pressure range of atmospheric pressure to 2 MPa.

Item 7.

The production method according to Item 5 or 6, further comprising:

-   -   (2) cooling the composition of the first stream obtained in        step (1) to induce liquid-liquid separation to form a phase A        containing a larger amount of water and a phase B containing a        larger amount of pentafluoropropane.

Item 8.

The method according to Item 7, further comprising: (3) subjecting thephase B separated in step (2) to step (1) as a composition comprisingpentafluoropropane and water.

Item 9.

The method according to any one of Items 5 to 8, wherein thepentafluoropropane is at least one pentafluoropropane selected from thegroup consisting of HFC-245cb, HFC-245eb, and1,1,1,3,3-pentafluoropropane (HFC-245fa).

Advantageous Effects of Invention

According to the method of the present invention, water can beefficiently removed from water-containing pentafluoropropane obtained byvarious synthesis methods, by performing distillation operation usingthe azeotropic phenomenon of pentafluoropropane and water, and furtherinducing liquid-liquid separation, if necessary.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a flow diagram showing the outline of operation in Examples 1and 2.

The azeotropic or azeotrope-like composition of the present invention,and the method for producing pentafluoropropane from which water isremoved are described in detail below.

In the present specification, the term “azeotropic composition” refersto a composition in which vapor balanced with a mixed liquid has thesame formulation as that of the mixed liquid. Specifically, this termrefers to a composition in which, when the liquid phase is a homogeneousphase, there is no pressure difference between the boiling point curveand the dew point curve (based on the pressure of the boiling pointcurve). In a heterophase azeotropic composition in which two liquidphases are formed, the two-liquid phase region shows a predeterminedvapor phase formulation; thus, the condensed liquid is considered to bean azeotropic composition. The term “azeotropic composition” in thepresent specification also includes a heterophase azeotropiccomposition.

In the present specification, the term “azeotrope-like composition”refers to a composition in which vapor balanced with a mixed liquid hasa similar formulation to that of the mixed liquid.

In the present specification, the terms “concentrate” and “remove” areused in opposing concepts. That is, when a component in a mixture isconcentrated, components other than this component are supposed to beremoved.

1. Azeotropic or Azeotrope-Like Composition

The azeotropic or azeotrope-like composition of the present inventioncomprises at least HFC-245cb or HFC-245eb, and water. The azeotropic orazeotrope-like composition of the present invention may consist ofHFC-245cb or HFC-245eb, and water; or may further contain otheradditional compounds, in addition to HFC-245cb or HFC-245eb, and water.

The study of the present inventors found a phenomenon in which when amixture of HFC-245cb or HFC-245eb, and water was distilled, water wasconcentrated toward the top of the distillation column, and when a fixedwater concentration was reached, the concentration did not increase anymore.

When the liquid phase is a homogeneous phase, the azeotrope-likecomposition of the present invention is preferably a composition inwhich the pressure difference between the boiling point curve and thedew point curve is within 5% (based on the pressure of the boiling pointcurve).

The additional compounds are not limited, and examples include saturatedor unsaturated halogenated hydrocarbons. The saturated or unsaturatedhalogenated hydrocarbons are preferably fluoridated hydrocarbon andchlorinated hydrocarbon, and more preferably C₁₋₃ fluoridatedhydrocarbon and chlorinated hydrocarbon.

Specific examples of the additional compounds include the followingcompound group. The azeotropic or azeotrope-like composition of thepresent invention may contain these compounds singly or in combinationof two or more (when HFC-245cb or HFC-245eb is not an essentialcomponent, these are contained as additional compounds in the azeotropicor azeotrope-like composition of the present invention).

-   -   CF₃CF═CH₂ (2,3,3,3-tetrafluoropropene, HFO-1234yf)    -   CF₃CH═CHF (1,3,3,3-tetrafluoropropene, HFO-1234ze)    -   CF₃CHFCH₃ (1,1,1,2,3-tetrafluoropropane, HFC-254eb)    -   CF₃CH═CH₂ (3,3,3-trifluoropropene, HFO-1243zf)    -   CF₃CHFCH₂F (1,2,3,3,3-pentafluoropropane, HFC-245eb)    -   CF₃CH₂CHF₂ (1,1,1,3,3-pentafluoropropane, HFC-245fa)    -   CF₃CF₂CH₃ (1,1,1,2,2-pentafluoropropane, HFC-245cb)    -   CF₃CHFCHF₂ (1,1,1,2,3,3-hexafluoropropane, HCFC-236ea)    -   CF₃CH₂CF₃ (1,1,1,3,3,3-hexafluoropropane, HFC-236fa)    -   CF₃CF═CHF (1,2,3,3,3-pentafluoropropene, HFO-1225ye)    -   CF₃CCH (3,3,3-trifluoropropyne)    -   CHF₃ (fluoromethane, HFC-23)    -   CH₂F₂ (difluoromethane, HFC-32)    -   CF₃CHF₂ (1,1,1,2,2-pentafluoroethane, HFC-125)    -   CF₃CH₂F (1,1,1,2-tetrafluoroethane, HFC-134a)    -   CF₃CF═CF₂ (hexafluoropropene, FC-1216)    -   CHCl₃ (trichloromethane)

For example, the azeotropic or azeotrope-like composition of the presentinvention is obtained by removing HF by water washing from a product ofreaction to obtain HFO-1234yf by HF elimination reaction of HFC-245cb orHFC-245eb, followed by distillation. In this example, HFO-1234zecontained in the azeotropic or azeotrope-like composition can serve asan additional compound.

The total content ratio of the additional compounds relative to theentire composition is preferably 10 mass % or less, more preferably 5mass % or less, and even more preferably 1 mass % or less. Theadditional compounds are generally contained in a total amount of 0.1mass % or more, preferably 0.01 mass % or more, and more preferably0.001 mass % or more.

In a preferable embodiment, the azeotropic or azeotrope-like compositionof the present invention consists of a two-component azeotropic orazeotrope-like composition consisting of HFC-245cb and water, and otheradditional compounds. In this embodiment, the total content ratio of theadditional compounds relative to the entire composition is preferably 5mass % or less, more preferably 1 mass % or less, and even morepreferably 0.5 mass % or less. Because the total content ratio of theadditional compounds is controlled within the above range, theazeotropic or azeotrope-like composition of the present inventionexhibits, as a whole, characteristics as an azeotropic or azeotrope-likecomposition.

In the azeotropic composition, the azeotropic formulation shows a fixedvalue depending on temperature and pressure. When temperature andpressure change, the azeotropic formulation may also change. Forexample, in a composition consisting of HFC-245cb and water, aformulation consisting of 99.12 mass % of HFC-245cb and 0.88 mass % ofwater is an azeotropic formulation at a pressure of 0.57 MPa and atemperature of 32° C. Further, in a composition consisting of HFC-245eband water, a formulation consisting of 75.5 mass % of HFC-245eb and 24.5mass % of water is an azeotropic formulation at a pressure of 0.129 MPaand a temperature of 25° C.

Moreover, formulations similar to the above formulations can be handledin the substantially same manner as azeotropic compositions (that is,compositions having such formulations are azeotrope-like compositions).

The two-component azeotropic or azeotrope-like composition consisting ofHFC-245cb and water more preferably contains 2 to 99.995 mass % or 96 to99.995 mass % of HFC-245cb relative to the entire two-componentcomposition. In this range, when the composition is azeotropic(including heterophase azeotropic), or when the liquid phase is ahomogeneous phase, within a pressure range of atmospheric pressure(0.1013 MPa) to 2 MPa, the pressure difference between the boiling pointcurve and the dew point curve is within 5%; that is, the compositionbecomes azeotrope-like (based on the pressure of the boiling pointcurve). Moreover, the two-component azeotropic or azeotrope-likecomposition more preferably further contains 95 to 100 mass % or 99 to100 mass % of HFC-245cb relative to the entire two-componentcomposition. In this range, when the composition is azeotropic(including heterophase azeotropic), or when the liquid phase is ahomogeneous phase, within a pressure range of atmospheric pressure(0.1013 MPa) to 2 MPa, the pressure difference between the boiling pointcurve and the dew point curve is within 5%; that is, the compositionbecomes more azeotrope-like (based on the pressure of the boiling pointcurve).

The two-component azeotropic or azeotrope-like composition consisting ofHFC-245eb and water more preferably contains 10 to 99.995 mass % or 98to 99.995 mass % of HFC-245eb relative to the entire two-componentcomposition. In this range, when the composition is azeotropic(including heterophase azeotropic), or when the liquid phase is ahomogeneous phase, within a pressure range of atmospheric pressure(0.1013 MPa) to 2 MPa, the pressure difference between the boiling pointcurve and the dew point curve is within 5%; that is, the compositionbecomes azeotrope-like (based on the pressure of the boiling pointcurve). Further, the two-component azeotropic or azeotrope-likecomposition more preferably contains 95 to 100 mass % or 99 to 100 mass% of HFC-245eb relative to the entire two-component composition. In thisrange, when the composition is azeotropic (including heterophaseazeotropic), or when the liquid phase is a homogeneous phase, within apressure range of atmospheric pressure (0.1013 MPa) to 2 MPa, thepressure difference between the boiling point curve and the dew pointcurve is within 5%; that is, the composition becomes more azeotrope-like(based on the pressure of the boiling point curve).

The distillation is preferably performed within a pressure range ofatmospheric pressure (0.1013 MPa) to 2 MPa. A pressure equal to orhigher than atmospheric pressure is preferable, because the refluxtemperature decreases, thereby reducing the possibility of liquidseparation in the column. Further, a pressure of 2 MPa or less ispreferable, because the operating temperature increases, and the heatingamount increases, thereby reducing the possibility of inefficiency.

2. Method for Producing Pentafluoropropane with Reduced Water Content

The method for producing pentafluoropropane with a reduced water contentof the present invention comprises:

-   -   (1) distilling a composition comprising pentafluoropropane and        water to thereby extract a pentafluoropropane-containing        composition with a water content higher than that of the        composition as a first stream, and a        pentafluoropropane-containing composition with a water content        lower than that of the composition as a second stream.

The pentafluoropropane is preferably at least one pentafluoropropaneselected from the group consisting of HFC-245cb, HFC-245eb, andHFC-245fa. The composition comprising pentafluoropropane and water maycontain one or more of these pentafluoropropanes.

The composition comprising pentafluoropropane and water preferablycontains at least one pentafluoropropane at a content ratio higher thanother pentafluoropropanes. In this case, in the composition comprisingpentafluoropropane and water, the total content ratio of the otherpentafluoropropanes relative to the entire composition is preferably 20mass % or less, more preferably 10 mass % or less, and even morepreferably 2 mass % or less. The at least one pentafluoropropane, whichis contained at a content ratio higher than other pentafluoropropanes,is preferably HFC-245cb.

The composition comprising pentafluoropropane and water may furthercontain the additional compounds described in section 1 above. In thiscase, when the composition comprising pentafluoropropane and watercontains at least one pentafluoropropane at a content ratio higher thanother pentafluoropropanes, the total content ratio of the additionalcompounds and the other pentafluoropropanes is preferably 10 mass % orless, more preferably 5 mass % or less, and even more preferably 1 mass% or less.

The distillation pressure is not limited, and can be set in a widerange. For example, the pressure can be set from about atmosphericpressure (0.1013 MPa) to 2 MPa. The distillation pressure is preferablyset in a range of 0.4 MPa to 2 MPa, because an overly low pressurelowers the reflux temperature, thereby reducing the possibility ofliquid separation in the column.

When the composition comprising pentafluoropropane and water, in whichthe water content is less than the above azeotropic formulation, isdistilled by this distillation operation, apentafluoropropane-containing composition with a concentrated watercontent, i.e., a pentafluoropropane-containing composition with a watercontent higher than that of the composition supplied to the distillationcolumn, is obtained from the column top of the distillation column(first stream).

When the pentafluoropropane-containing composition with a concentratedwater content (first stream) obtained from the column top in step (1) isdried using an adsorbent, such as a molecular sieve, the size of thedrying column necessary for drying can be reduced, compared withconventional drying methods.

The pentafluoropropane-containing composition with a reduced watercontent (second stream) obtained from the column bottom in step (1) canalso be dried using an adsorbent, such as a molecular sieve.

When the composition comprising pentafluoropropane and water isdistilled, the additional compounds can be extracted together withpentafluoropropane, and separated in another distillation column.

The production method of the present invention may further comprise thefollowing step (2), if necessary:

-   -   (2) cooling the composition of the first stream obtained in        step (1) to induce liquid-liquid separation to form a phase A        containing a larger amount of water and a phase B containing a        larger amount of pentafluoropropane.

Thus, the pentafluoropropane-containing composition (first stream)obtained from the column top is cooled using a decanter or the like toinduce liquid-liquid separation to form a phase A containing a largeramount of water and a phase B containing a larger amount ofpentafluoropropane, whereby water can be efficiently separated.

In the decanter, liquid-liquid separation may occur by cooling to atemperature lower than the pentafluoropropane-containing compositionextracted from the distillation column. The temperature can be widelyselected within a range in which the separated water does not freeze.For example, the temperature can be set to 5 to 50° C.

Water can be efficiently separated by performing the above distillationoperation and liquid-liquid separation as a continuous operation.

The phase A containing a large amount of water separated in the abovemanner may be discarded. Further, the phase B containing a larger amountof pentafluoropropane can be returned to the rectification column andrectified again. When only the phase B is dried by a molecular sieve,the size of the drying column necessary for drying can be significantlyreduced.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in more detail below with referenceto Examples.

EXAMPLE 1

Table 1 shows the data of the phase equilibrium between HFC-245cb andwater at 0.57 MPa.

TABLE 1 x(245cb) y(245cb) T(° C.) 0.0 0 157.0 5.0 99.12 32.0 10.0 99.1232.0 20.0 99.12 32.0 30.0 99.12 32.0 40.0 99.12 32.0 50.0 99.12 32.060.0 99.12 32.0 70.0 99.12 32.0 80.0 99.12 32.0 90.0 99.12 32.0 99.099.12 32.0 99.75 99.17 32.0 99.84 99.48 32.1 99.90 99.67 32.2 99.9699.87 32.2 100.0 100.0 32.3

As shown in Table 1, it is found that there are two phases in theformations in which the 245cb ratio is between 5% and 99%.

Table 2 shows the results of distilling HFC-245cb containing water withan inlet water concentration of 200 ppm using a distillation columnhaving a theoretical plate number of 20. FIG. 1 shows a schematicdiagram of the distillation column. The pressure was 0.57 MPa, thecolumn top temperature was 32° C., and the column bottom temperature was35° C. In FIG. 1 , F11 represents the supplied gas, and S11 to S14represent streams.

TABLE 2 Water concentration (unit: mass) F11 S11 S12 S13 S14 200 ppm3500 ppm <1 ppm >99% 2600 ppm

-   -   Operating pressure: 0.47 MPaG    -   Top temperature: 32° C.    -   Bottom temperature: 35° C.

EXAMPLE 2

Table 3 shows the data of the phase equilibrium between HFC-245eb andwater at 25° C.

TABLE 3 x(245eb) y(245eb) P(MPa) 0.0 0 −0.098 1.0 75.5 −0.069 2.0 75.5−0.050 5.0 75.5 −0.02 10.0 75.5 0.129 20.0 75.5 0.129 30.0 75.5 0.12940.0 75.5 0.129 50.0 75.5 0.129 60.0 75.5 0.129 70.0 75.5 0.129 80.075.5 0.129 90.0 75.5 0.129 98.0 75.5 0.12 99.9 99.5 0.115 100.0 1000.113

Because the vapor pressure of the compositions of 245eb and water ishigher than that of each pure substance, it is found that thesecompositions are azeotropic. At least the formulations in which the245eb ratio is between 10% and 90% are considered to be heterophaseazeotropic.

REFERENCE SIGNS LIST

-   -   1. Rectification column    -   2. Reboiler    -   3. Capacitor    -   4. Decanter

1-9. (canceled)
 10. A method for producing a composition comprisingpentafluoropropane with a water content lower than that of a startingcomposition comprising pentafluoropropane and water, the methodcomprising: (1) distilling the starting composition to thereby extract apentafluoropropane-containing composition with a water content higherthan that of the starting composition as a first stream, and apentafluoropropane-containing composition with a water content lowerthan that of the starting composition as a second stream.
 11. The methodaccording to claim 10, wherein the distillation is performed within apressure range of atmospheric pressure to 2 MPa.
 12. The productionmethod according to claim 10, further comprising: (2) cooling thecomposition of the first stream obtained in step (1) to induceliquid-liquid separation to form a phase A containing a larger amount ofwater and a phase B containing a larger amount of pentafluoropropane.13. The method according to claim 12, further comprising: (3) subjectingthe phase B separated in step (2) to step (1) as a compositioncomprising pentafluoropropane and water.
 14. The method according toclaim 10, wherein the pentafluoropropane is at least onepentafluoropropane selected from the group consisting of HFC-245cb,HFC-245eb, and 1,1,1,3,3-pentafluoropropane (HFC-245fa).
 15. Theproduction method according to claim 11, further comprising: (2) coolingthe composition of the first stream obtained in step (1) to induceliquid-liquid separation to form a phase A containing a larger amount ofwater and a phase B containing a larger amount of pentafluoropropane.16. The method according to claim 15, further comprising: (3) subjectingthe phase B separated in step (2) to step (1) as a compositioncomprising pentafluoropropane and water.
 17. The method according toclaim 11, wherein the pentafluoropropane is at least onepentafluoropropane selected from the group consisting of HFC-245cb,HFC-245eb, and 1,1,1,3,3-pentafluoropropane (HFC-245fa).
 18. The methodaccording to claim 12, wherein the pentafluoropropane is at least onepentafluoropropane selected from the group consisting of HFC-245cb,HFC-245eb, and 1,1,1,3,3-pentafluoropropane (HFC-245fa).
 19. The methodaccording to claim 13, wherein the pentafluoropropane is at least onepentafluoropropane selected from the group consisting of HFC-245cb,HFC-245eb, and 1,1,1,3,3-pentafluoropropane (HFC-245fa).
 20. The methodaccording to claim 15, wherein the pentafluoropropane is at least onepentafluoropropane selected from the group consisting of HFC-245cb,HFC-245eb, and 1,1,1,3,3-pentafluoropropane (HFC-245fa).
 21. The methodaccording to claim 16, wherein the pentafluoropropane is at least onepentafluoropropane selected from the group consisting of HFC-245cb,HFC-245eb, and 1,1,1,3,3-pentafluoropropane (HFC-245fa).